LOS ANGELES, Aug. 22 (Xinhua) -- As many as 50 people were injured after a tour bus overturned on a major highway to east Los Angeles Thursday morning, authorities said.

The bus rolled over around 10 a.m. local time near Irwindale Avenue along the Foothill Freeway (Interstate 210), about 32 km east of downtown Los Angeles, Los Angeles County Fire Department said.

Six of those who suffered serious injuries were airlifted to trauma centers in nearby areas, but none of them were listed as life-threatening, authorities said.

At least 10 ambulances and four medical helicopters rushed to the scene. All lanes of the highway on both directions were temporarily closed. An hour later, all westbound lanes and the eastbound carpool lane were reopened.

The vehicle, belonging to the Da Zhen Travel Agency based in Monterey Park, was heading to the San Miguel Indian Bingo and Casino in San Bernardino at the time of the crash, local media reported.

An investigation into the cause of the accident is underway.